docs: def from_arrays(cls, **kwargs):
          '''Initialize a System from its constituent arrays. It is the
          fastest way to initialize a System, well suited for 
          reading one or more big System from data files.
  
          **Parameters**
          
          The following parameters are required:
          
          - type_array: An array of the types
          - maps: A dictionary that describes the relationships between 
                  molecules in the system and atoms and bonds.
          
          **Example**
          
          This is how to initialize a System made of 3 water molecules::
  
                  # Initialize the arrays that contain 9 atoms
                  r_array = np.random.random((3, 9))
                  type_array = ['O', 'H', 'H', 'O', 'H', 'H', 'O', 'H', 'H']
                  
                  # The maps tell us to which molecule each atom belongs to. In this 
                  # example first 3 atoms belong to molecule 0, second 3 atoms
                  # to molecule 1 and last 3 atoms to molecule 2.
                  maps = {('atom', 'molecule') : [0, 0, 0, 1, 1, 1, 2, 2, 2]}
                  System.from_arrays(r_array=r_array, 
                                     type_array=type_array,
                                     maps=maps)
                  
                  # You can also specify bonds, again with the its map that specifies
                  # to to which molecule each bond belongs to.
                  bonds = [[0, 1], [0, 2], [3, 4], [3, 5], [6, 7], [6, 8]]
                  maps[('bond', 'molecule')] = [0, 0, 1, 1, 2, 2]
                  System.from_arrays(r_array=r_array, 
                                     type_array=type_array,
                                     bonds=bonds,
                                     maps=maps)
                  
  
          '''
          if 'mol_indices' in kwargs:
              raise DeprecationWarning('The mol_indices argument is deprecated, use maps instead. (See from_arrays docstring)')
          
          return super(System, cls).from_arrays(**kwargs)